1. Field of Invention
The present invention relates in general to a control device for controlling an internal combustion engine, and more particularly to a variable valve control device of an internal combustion engines, which comprises a working angle varying mechanism for varying a working angle of the intake or exhaust valve and an operation phase varying mechanism for varying an operation phase of the intake or exhaust valve.
2. Description of Related Art
Hitherto, various types of variable valve control devices have been proposed and put into practical use in the field of automotive internal combustion engines. One of such devices is shown in an instruction manual of Toyota car (ALTEZZA) issued on October, 1998 from Toyata Jidosha Kabushiki Kaisha, which comprises generally a so-called intake valve operation phase varying mechanism which varies the operation phase of each intake valve by changing a relative angular position between an intake valve cam shaft and a cam pulley synchronously rotated with the engine crankshaft, and a so-called exhaust valve operation phase varying mechanism which varies the operation phase of each exhaust valve by changing a relative angular position between an exhaust valve cam shaft and the above-mentioned cam pulley. The intake and exhaust valve operation phase varying mechanisms are both powered commonly by a hydraulic pressure produced by an oil pump driven by the engine crankshaft.
It is now to be noted that the term xe2x80x9coperation phasexe2x80x9d used in the description corresponds to the operation timing of the corresponding intake or exhaust valve with respect to that of the engine crankshaft, and the term xe2x80x9cworking anglexe2x80x9d used in the description corresponds to the open period of the corresponding intake or exhaust valve and is represented by an angle range (viz., crank angle) of the engine crankshaft.
In general, when, in a middle-load operation range of the engine, a certain valve overlap is provided at or near the top dead center (TDC) on the intake stroke, a certain amount of internal EGR is obtained, which induces reduction in pumping loss and improvement in fuel consumption and exhaust performance. Furthermore, when, in the middle-load operation range, a certain minus valve overlap is provided, a certain amount of exhaust gas is confined in the combustion chamber, which induces reduction in pumping loss and improvement in fuel consumption. It is to be noted that the valve overlap is a phenomenon wherein both the intake and exhaust valves show their open condition simultaneously for a certain time, and the minus valve overlap is a phenomenon wherein both the intake and exhaust valves show their closed condition simultaneously for a certain time.
While, in a very low load operation range, such as in the operation range at the time of engine idling, it is necessary to remove or at least minimize the valve overlap and/or minus valve overlap in order to suppress unstable combustion caused by the residual gas of the internal EGR. Accordingly, in case of shifting from the middle-load operation range to the very low-load operation range, such as, in case of rapid deceleration of the engine speed, speedy reduction or cancellation of the valve overlap or minus valve overlap is needed.
Accordingly, an object of the present invention is to provide an intake valve control device of an internal combustion engine, which comprises operation phase varying mechanisms for varying an operation phase of the intake and exhaust valves respectively and a working angle varying mechanism for varying a working angle of the intake or exhaust valve, so that in case of engine operation change from a middle-load operation range to a very low-load operation range, reduction or cancellation of the valve overlap and/or minus valve overlap is assuredly and speedily carried out.
In order to embody the present invention, the following facts have been seriously considered by the applicants.
In a working angle varying mechanism, the biasing force of each valve spring affects to operation of the mechanism. That is, the opening action of the valve is carried out against the biasing force of the valve spring and the closing action of the valve is carried out with the aid of the biasing force. This means that in case of reducing the working angle of the valve, the work of the mechanism is assisted by the biasing force of the valve spring. Thus, under the same hydraulic power applied to the mechanism, responsiveness in such working angle reducing case is higher than that in case of increasing the working angle.
While, in an operation phase varying mechanism, a torque is applied to a drive shaft or cam shaft which drives the valve to open and close the same. This means that in case of retarding the operation phase, the work of the mechanism is assisted by the torque. Thus, under the same hydraulic power applied to the mechanism, responsiveness in such operation phase retarding case is higher than that in case of advancing the operation phase.
That is, the degree of the responsiveness is represented by the following order.
Slow: Increasing a working angle by using the working angle varying mechanism.
Slightly fast: Advancing an operation phase by using the operation phase varying mechanism.
Fast: Retarding an operation phase by using the operation phase varying mechanism.
Very fast: Reducing a working angle by using the working angle varying mechanism.
Taking these facts into consideration, the present invention provides a variable valve control device of an internal combustion engine, which, in case of the shifting from the middle-load operation range to the very low-load operation range, selectively operates the operation phase and working angle varying mechanisms in a manner to effectively and speedily reduce or cancel the valve overlap or minus valve overlap.
According to a first aspect of the present invention, there is provided a variable valve control device of an internal combustion engine having intake and exhaust valves. The control device comprises an IVWAV mechanism which varies a working angle of the intake valve; an IVOPV mechanism which varies an operation phase of the intake valve; an EVOPV mechanism which varies an operation phase of the exhaust valve; and a control unit which controls the IVWAV, IVOPV and EVOPV mechanisms in accordance with an operation condition of the engine, the control unit being configured to carry out controlling, in a middle-load operation range of the engine, the IVWAV, IVOPV and EVOPV mechanisms to achieve a valve overlap wherein near the top dead center (TDC) on the intake stroke, there is a certain period when both the intake and exhaust valves assume their open conditions, and in case of shifting of the engine from the middle-load operation range to a very low-load operation range, controlling the IVWAV mechanism to reduce the working angle of the intake valve thereby to retard the open timing of the intake valve and controlling the EVOPV mechanism to advance the operation phase of the exhaust valve thereby to advance the close timing of the exhaust valve.
According to a second aspect of the present invention, there is provided a variable valve control device of an internal combustion engine having intake and exhaust valves. The control device comprises an IVWAV mechanism which varies a working angle of the intake valve; an IVOPV mechanism which varies an operation phase of the intake valve; an EVOPV mechanism which varies an operation phase of the exhaust valve; and a control unit which controls the IVWAV, IVOPV and EVOPV mechanisms in accordance with an operation condition of the engine, the control unit being configured to carry out controlling, in a middle-load operation range of the engine, the IVWAV, IVOPV and EVOPV mechanisms to achieve a minus valve overlap wherein near the top dead center on the intake stroke, there is a certain period when both the intake and exhaust valves assume their close conditions; and in case of shifting of the engine from the middle-load operation range to a very low-load operation range, controlling the IVOPV mechanism to advance the operation phase of the intake valve thereby to advance the open timing of the intake valve and controlling the EVOPV mechanism to retard the operation phase of the exhaust valve thereby to retard the close timing of the exhaust valve.
According to a third aspect of the present invention, there is provided a variable valve control device of an internal combustion engine having intake and exhaust valves. The control device comprises an IVOPV mechanism which varies an operation phase of the intake valve; an EVWAV mechanism which varies a working angle of the exhaust valve; an EVOPV mechanism which varies an operation phase of the exhaust valve; a control unit which controls the IVOPV, EVWAV and EVOPV mechanisms in accordance with an operation condition of the engine, the control unit being configured to carry out controlling, in a middle-load operation range of the engine, the IVOPV, EVWAV and EVOPV mechanisms to achieve a minus valve overlap wherein near the top dead center on the intake stroke, there is a certain period when both the intake and exhaust valves assume their close conditions; and in case of shifting of the engine from the middle-load operation range to a very low-load operation range, controlling the IVOPV mechanism to advance the operation phase of the intake valve thereby to advance the open timing of the intake valve and controlling the EVOPV mechanism to retard the operation phase of the exhaust valve thereby to retard the close timing of the exhaust valve.
According to a fourth embodiment of the present invention, there is provided a variable valve control device of an internal combustion engine having intake and exhaust valves. The control device comprises at least one of IVWAV and EVWAV mechanisms, the IVWAV mechanism functioning to vary a working angle of the intake valve and the EVWAV mechanism functioning to vary a working angle of the exhaust valve; an IVOPV mechanism which varies an operation phase of the intake valve; an EVOPV mechanism which varies an operation phase of the exhaust valve; and a control unit which controls the selected one of the IVWAV and EVWAV mechanisms and the IVOPV and EVOPV mechanisms in accordance with an operation condition of the engine, the control unit being configured to carry out controlling, in a middle-loaded operation range of the engine, the selected one of the IVWAV and EVWAV mechanisms and the IVOPV and EVOPV mechanisms to achieve a valve overlap or a minus valve overlap near the top dead center (TDC) on the intake stroke, and in case of shifting of the engine from the middle-load operation range to a very low-load operation range, controlling the IVWAV mechanism or the IVOPV mechanism to shift the open timing of the intake valve toward the top dead center (TDC) on the intake stroke, and controlling the EVWAV mechanism or EVOPV mechanism to shift the close timing of the exhaust valve toward the top dead center (TDC) on the intake stroke.